Technical Field
The present disclosure relates to a method for the concurrent production of algae and the separation of gold from a gold ore using an algal mat and a system for the production of algae and the separation of gold from a gold ore using an algal mat.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Algae thrive in turbid, brackish water environments with little more than basic nutrients and sunshine. They grow far more rapidly than conventional crops, and generate a much higher fraction of their biomass as oil (up to 60%, versus 2%-3% for soybeans).
As recently, algae have become significant organisms for biological purification of wastewater since they are able to accumulate plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances and radioactive matters in their cells/bodies (Kalesh N S, Nair S M The Accumulation Levels of Heavy Metals (Ni, Cr, Sr, & Ag) in Marine Algae from Southwest Coast of India. Toxicological & Environmental Chemistry 2005; 87(2): 135-146; Jothinayagi N, Anbazhagan C. Heavy Metal Monitoring of Rameswaram Coast by Some Sargassum species. American-Eurasian Journal of Scientific Research 2009; 4 (2): 73-80; Alp M T, Sen B, Ozbay O. Heavy Metal Levels in Cladophora glomerata which Seasonally Occur in the Lake Hazar. Ekoloji, 20 (78): 13-17. doi: 10.5053/ekoloji.2011.783; Alp M T, Ozbay O, Sungur M. A. Determination of Heavy Metal Levels in Sediment and Macroalgae (Ulva sp. and Enteromorpha sp.) on the Mersin Coast 2011. Ekoloji 21, 82, 47-55 (2012)—each incorporated herein by reference in its entirety). These specific features have made algal wastewater treatment systems a significant low-cost alternative to complex expensive treatment systems particularly for purification of municipal wastewaters.
In addition, algae harvested from treatment ponds are widely used as nitrogen and phophorus supplements for agricultural purpose and can be subjected to fermentation in order to obtain energy from methane. Algae are also able to accumulate highly toxic substances such as selenium, zinc and arsenic in their cells and/or bodies thus eliminating such substances from aquatic environments. Radiation is also an important type of pollution as some water contains naturally radioactive materials, and others become radioactive through contamination. Many algae can take up and accumulate many radioactive minerals in their cells even from greater concentrations in the water (Palmer, C. M. A composite rating of algae tolerating organic pollution. J. Phycology. 1969; 5: 78-82—incorporated herein by reference in its entirety). MacKenthun emphasized that Spirogyra can accumulate radio-phosphorus by a factor 850,000 times that of water (MacKenthun, K. M. Radioactive wastes. Chapt 8. In The Practice of Water Pollution Biology. U.S. Dept. Interior, Fed. Water Pol. Contr. Admin., Div. of Tech. Support.U.S. Printing Office 1969—incorporated herein by reference in its entirety).
It is well known that algae have an important role in self-purification of organic pollution in natural waters (Sen, B. ve Nacar, V. Su Kirlili{hacek over (g)}i ve Algler. Firat Havzasi I. Cevre Sempozyumu Bildiriler Kitabi. 1988; 405-21—incorporated herein by reference in its entirety). Moreover, many studies revealed that algae remove nutrients especially nitrogen and phosphorus, heavy metals, pesticides, organic and inorganic toxins, pathogens from surrounding water by accumulating and/or using them in their cells (Reddy, K. R. Fate of Nitrogen and Phosphorus in a Wastewater Retention Reservoir Containing Aquatic Macrophytes. Journal of Environmental Quality, 1983; 12(1):137-41; Lloyd, B. J. and Frederick, G. L. Parasite removal by waste stabilisation pond systems and the relationship between concentrations in sewage and prevalence in the community, Water Science and Technology 2000; 42(10):375-86—each incorporated herein by reference in its entirety). Also, studies showed that algae may be used successfully for wastewater treatment as a result of their bioaccumulation abilities (Oswald, W. J. The role of microalgae in liquid waste treatment and reclamation. In: C. A. Lembi and J. R. Waalnd (eds). Algae and Human Affairs, Cambridge University Press 1988a; 403-31—incorporated herein by reference in its entirety).
Wastewater treatment systems which are applied to improve or upgrade the quality of a wastewater involves physical, chemical and biological processes in primary, secondary or tertiary stages. Primary treatment removes materials that will either float or readily settle out by gravity. It includes the physical processes of screening, contamination, grit removal, and sedimentation. While the secondary treatment is usually accomplished by biological processes and removes the soluble organic matter and suspended solids left from primary treatment. Tertiary or advanced treatment is process for purification in which nitrates and phosphates, as well as fine particles are removed (Droste, R. L. Theory and Practice of water and wastewater treatment, John Wiley and Sons, New York 1997—incorporated herein by reference in its entirety). However initial cost as well as operating cost of wastewater treatment plant including primary, secondary or advanced stages is highly expensive (Oswald,W. J. Ponds in twenty first century. Water Science and Technology 1995; 31(12):1-8—incorporated herein by reference in its entirety).
Some algae produce lipids that can be converted to biodiesel or green diesel. Some strains produce ethanol. Algae biomass is also used as food, animal feed and fertiliser, but it isn't reasonable to expect 100% substitution—there are too many complications. In 20 years fuel substitution is expected to be in the 5%-8% range.
Creating biofuels from microbes has many advantages. Algae can grow in low lying areas unsuitable for conventional crops. Algae can yield 8,000 litres of fuel per acre per year, compared with 2,600 litres for palm oil and 200 litres for soy. Algae can use brackish water or wastewater as a growing medium, eliminating the freshwater needs of ethanol production. Algae production does not compete with food crops such as corn or soy for acreage, nutrients or fresh water. Furthermore, biofuels are similar enough to gasoline and diesel that they do not require special treatment during transportation and mixing at the refinery.
Recent studies conclude that this algae dewatering process costs over $3,000 in energy alone to produce one ton of dry weight biomass equivalent, making algae an uneconomic source of fuel when compared to fossil fuels. Nevertheless, a comprehensive industry survey undertaken by the Algal Biomass Organization last year found that more than 35% of industry participants believe it is either very likely or extremely likely that algae-based fuels will be cost-competitive with fossil fuels by 2020.